In a series of experiments the proposed research will examine the role of both environmental and physiological factors in the control of sexual receptivity (behavioral estrus) in the female golden hamster. Mechanisms underlying both the initiation and termination of receptivity will be examined with particular emphasis on changes in the receptivity of the female following mating. The first phase of the study will examine the stimuli associated with the male hamster which are capable of altering the duration of behavioral estrus. Various experimental techniques for limiting the stimulation received by the female (for example genital desensitization) will be examined. The second phase of the research will investigate physiological changes in the female which may result from the interaction of a male and a female during mating. Initial experiments will focus on the role of ovarian hormones in the regulation of the duration of estrus. The behavior of females ovariectomized and/or receiving exogenous hormones will be observed.